Television ratings and metering information is typically generated by collecting viewing records and/or other viewing information from a group of statistically selected households. Each of the statistically selected households typically has a data logging and processing unit commonly referred to as a “home unit.” In households having multiple viewing sites (e.g., multiple television systems), the data logging and processing functionality may be distributed among a single home unit and multiple “site units,” one site unit for each viewing site. The home unit (or the combination of the home unit and the site unit) is often in communication with a variety of attachments that provide inputs to the home unit or receive outputs from the home unit. For example, a source identification unit such as a frequency detector attachment may be in communication with a television to sense a local oscillator frequency of the television tuner. In this manner, the frequency detector attachment may be used to determine the channel to which the television is currently tuned based on a detected frequency. Additional source identification devices, such as on-screen readers and light-emitting-diode (LED) display readers, may be provided, for example, to determine if the television is operating (i.e., is turned ON) and/or the channel to which the television is tuned. A people counter may also be located in the viewing space of the television and in communication with the home unit, thereby enabling the home unit to detect the identities and/or number of the persons currently viewing programs displayed on the television.
The home unit usually processes the inputs (e.g., channel tuning information, viewer identities, etc.) from the attachments to produce viewing records. Viewing records may be generated on a periodic basis (i.e., at fixed time intervals) or may be generated in response to a change in an input, such as a change in the identities of the persons viewing the television, a change in the channel tuning information (i.e., a channel change), etc. Each viewing record typically contains channel information, such as a channel number and/or station identification (ID), and a time (e.g., a date and time-of-day) at which the channel was displayed. In cases in which the program content being displayed is associated with a local audio/video content delivery device, such as a digital video disk (DVD) player, a digital video recorder (DVR), a video cassette recorder (VCR), etc., the viewing records may include content identification (i.e., program identification) information as well as information relating to the time and manner in which the associated content was displayed. Viewing records may also contain additional information, such as the number of viewers present at the viewing time.
The home unit typically collects a quantity of viewing records and periodically transmits the collected viewing records (e.g., daily) to a central office or data processing facility for further processing or analysis. The central data processing facility receives viewing records from home units located in some or all of the statistically selected households and analyzes the viewing records to ascertain the viewing behaviors of households in a geographic area or market of interest, a particular household and/or a particular group of households selected from all participating households. Additionally, the central data processing facility may generate metering statistics and other parameters indicative of viewing behavior associated with some or all of the participating households. This data may be extrapolated to reflect the viewing behaviors of markets and/or regions modeled by the statistically selected households.
To generate viewing behavior information from viewing records, the central office or data processing facility may compare reference data, such as a list of programs (e.g., a schedule of television programming or a television guide), to the viewing records. In this manner, the central office can infer which program was displayed by cross-referencing the time and channel information in a viewing record to the program associated with that same time and channel in the program schedule. Such a cross-referencing process can be carried out for each of the viewing records received by the central office, thereby enabling the central office to reconstruct which programs were displayed by the selected households and the times at which the programs were displayed. Of course, the aforementioned cross-referencing process is unnecessary in systems in which the identity of the program is obtained by the home unit and contained in the viewing record.
The rapid development and deployment of a wide variety of audio/video content delivery and distribution platforms has dramatically complicated the home unit task of providing viewing records or information to the central data collection facility. For instance, while the above-mentioned frequency detector device can be used to detect channel information at a site where network television broadcasts are being displayed (because, under normal operation conditions, the local oscillator frequency corresponds to a known network channel), such a device typically cannot be used with digital broadcast systems. In particular, digital broadcast systems (e.g., satellite-based digital television systems, digital cable systems, etc.) typically include a digital receiver or set-top box at each subscriber site. The digital receiver or set-top box demodulates a multi-program data stream, parses the multi-program data stream into individual audio and/or video data packets, and selectively processes those data packets to generate an audio/video signal for a desired program. The audio and/or video output signals generated by the set-top box can be directly coupled to an audio/video input of an output device (e.g., a television, a video monitor, etc.) As a result, the local oscillator frequency of the output device tuner, if any, does not necessarily have any meaningful relationship to the channel or program currently being displayed.
To allow generation of meaningful viewing records in cases wherein, for example, the network channel is not readily identifiable or may not uniquely correspond to a displayed program, metering techniques based on the use of ancillary codes and/or content signatures may be employed. Metering techniques that rely on ancillary codes often encode and embed identifying information (e.g., a broadcast/network channel number, a program identification code, a broadcast time stamp, a source identifier to identify a network and/or station providing and/or broadcasting the content, etc.) in the broadcast signal such that the code is not noticed by the viewer. For example, a well-known technique used in television broadcasting involves embedding the ancillary codes in the non-viewable vertical blanking interval of the video signal. Another example involves embedding the ancillary codes in non-audible portions of the audio signal accompanying the broadcast program. This latter technique is especially advantageous because the ancillary code may be reproduced by, for example, the television speaker and non-intrusively monitored by an external sensor, such as a microphone.
In general, signature-based program identification techniques use one or more characteristics of the currently displayed (but not yet identified) audio/video content to generate a substantially unique proxy or signature (e.g., a series of digital values, a waveform, etc.) for that content. The signature information for the content being displayed may be compared to a set of reference signatures corresponding to a known set of programs. When a substantial match is found, the currently displayed program content can be identified with a relatively high probability.
While the known apparatus and techniques described above are well suited for generating viewing records associated with live viewing of television programming, these techniques are not directly applicable to the generation of viewing records associated with time-shifted viewing of program content (i.e., viewing a previously recorded program at a time later than the original broadcast time or, in other words, viewing a time-shifted broadcast program). In particular, local sources, such as DVD players, personal video recorders (PVRs), DVRs, VCRs and the like, enable the recording and playback of program content at various times other than the original broadcast time and in different manners across the statistically selected households. As a result, viewing records containing only viewing time information (and not original broadcast time information) cannot be compared to reference program guide information at the central office to infer which programs are associated with the viewing records. Further, the tuning information available from, for example, a frequency detector attachment in communication with a television that is being used to display a previously recorded program may not provide useful network channel information. More specifically, the recorded program is typically supplied by a video recorder (e.g., a VCR) or the like that sends unmodulated low-level video and audio signals to the video and audio inputs of the television that bypass the tuner circuitry of the television. The use of DVRs and PVRs, such as the TiVo™ system, further complicates the collection of viewing behavior information because viewers in households with these types of recording devices can rapidly alternate between live viewing of a program, a somewhat delayed viewing of a program, fast-forwarding and rewinding a program, pausing a program, and recording a program for later viewing while watching a live broadcast of another program.